Project Summary Substance use disorders are a significant public health issue, costing tens of thousands of lives and hundreds of billions of dollars annually . Considerable efforts have been expended to elucidate the neural mechanisms underpinning the acute and chronic actions of drugs of abuse on the nervous system, with the hope that better understanding of these mechanisms will lead to novel therapeutics. Much of this research has targeted receptors on neurons that are localized to cell bodies, axons, or dendrites; however, neurons also contain primary cilia, which are microtubule-based organelles that project from the cell bodies of all neurons. The importance of cilia function for human health is highlighted by the number of diseases caused by cilia dysfunction, several of which are associated with cognitive and motivational deficits. Neuronal cilia express a variety of G protein-coupled receptors (GPCRs), several of which are rarely expressed outside of cilia. Notably, several of these receptors, including the receptor for melanin-concentrating hormone (MCHR1) and the orphan GPCR, GPR88, have been shown to modulate responses to drugs of abuse. Despite what we know about cilia, our understanding of how cilia regulate neuronal function and behavior is still limited, and, in particular, there has been no prior research on interactions between neuronal cilia and drugs of abuse. The long-term goal of this research is to determine how ciliary signaling contributes to integration of neuromodulatory signals that regulate short- and long-term responses to drugs of abuse. As a first step toward this goal, the objective of our R21 proposal is to determine the role of primary cilia on dopaminergic and GABAergic neurons in the VTA and nucleus accumbens, respectively, in regulation of cocaine-induced behavioral plasticity and reward. This will be accomplished through molecular-genetic approaches to target cilia loss on specific neuronal types, in combination with behavioral pharmacological approaches. The proposed experiments will allow us to test our central hypothesis that neuronal cilia within mesolimbic circuitry are critical regulators of cocaine-induced plasticity and reward. We will test this hypothesis through two Specific Aims. Experiments in Aim 1 will use novel transgenic mouse strains to determine a) how cilia loss on dopaminergic and/or GABAergic neurons affects locomotion and locomotor sensitization induced by acute and repeated cocaine, respectively; b) whether locomotor alterations can be rescued by virally- mediated restoration of cilia in targeted brain regions, and c) how repeated cocaine alters cilia morphology and MCHR1 and GPR88 expression in mesolimbic brain regions. Experiments in Aim 2 will use similar approaches to determine whether cilia on dopaminergic and/or GABAergic neurons are necessary and sufficient for the rewarding effects of cocaine using a conditioned place preference task. The proposed research is innovative, as neuronal cilia have heretofore not been assessed in the context of drugs of abuse. The proposed research is significant, as cilia represent a unique neuronal signaling environment, a better understanding of which could lead to novel targets for therapies aimed at reducing substance use.